How small vertical loss rates can lead to exceptional high primary production in a stratified coastal system

Primary production, zooplankton biomass and activity, sedimentation processes and nutrient conditions was followed frequently during two years (1998 and 1999) in a stratified silt fjord (Mariager Fjord) in Denmark. Because of general low sedimentation- and grazing rates, very high phytoplankton biomass was achieved (ca. 100 ug Chl l-1). The system was characterized by continuously rises and falls of blooms throughout the productive season. The peaks, which were rather mono specific, didn't always correlated with the availability of nutrients, but seems also to be governed of pH and lysis. The high obtained concentration of phytoplankton allowed an efficient exploitation of the incoming solar radiation, resulting in some of the highest primary production rates ever measured in natural temperate waters (1000 g C m-2 y-1). The low sedimentation rates (< 1 m d-1) even during the decreases of biomass following the peaks, was ascribed an unexpected low aggregation. Since the physical conditions for collision among the particles was present, the lack of aggregation seems to be related to low stickiness. It is speculated whether a virus-bacteria dominated community can attribute to this.